Can Betta Fish Change Gender?

The splendid and fiery betta breed has fascinated fish keepers for over 1,000 years. The males, particularly, are as aggressive as they are graceful and beautiful. Because fish enthusiasts favor the showy male, many researchers have attempted to decode the Siamese fighter fish’s sex determination process. Part of that research was affecting gender reversal on female betta fish.

Betta fish can change gender from female to male and produce viable offspring. Reversed ‘Neomale’ bettas develop a teste-like organ that functions as a gonad and creates sperm to fertilize female bettas eggs. However, this is unlikely to occur spontaneously without intensive hormonal treatments.

The sex determination process in the beta is not primarily genetic and includes environmental and hormonal aspects of betta physiology. Although many betta experts claim to witness sex reversal in their fish, the likelihood of this reversal occurring is extremely unlikely. But is it possible? Read on to find out!

Purple and Blue Betta

Betta Fish and Sex Determination

In a manner that would make Darwin smile from (heaven or hell according to your religious affiliations), the ornamental betta fish has undergone rapid evolutionary changes from the wild.

Two independent studies of betta ornamental and wild populations conducted in China and UC Berkeley came up with a groundbreaking find. Over the 1000 years of domestication, the ornamental betta has evolved a sex gene called the DMRT1.

Bettas and the DMRT1 Sex Gene 

The DMRT1 gene has two versions of alleles: the Y chromosome found in males and the X located in both males and females. However, male bettas outside of hormonal manipulation have been found to have XX chromosomes, and females have the male XY chromosome. This evidence shows that genes are not the only determiner of sex in betta fish.

Environment and Betta Sex Determination

The above study suggests sex determination in bettas is more complex and be influenced by environmental factors. A recent study of the effects of temperature in sex determination in betta fry found that larvae raised in the temperature range of 25-30ºC produced the highest ratio of male fry, at 67%.

Hormone Induced Sex Reversal in Betta females 

In a study conducted in 1988, researchers removed the ovaries and gave female bettas testosterone injections over nine weeks. They observed that the females changed fin length body coloration and developed male gonads. They also exhibit the behavioral characteristics of male aggression.

Almost half of the females reversed into males, complete with functioning sex organs and sperm production. Once they mated the neo males with female bettas, 3 out of 11 spawnings created both female and male offspring.

Because the reversed females produced both males and females, the study suggests that part of the betta’s brain determines its sex. Once triggered as a female, the sex is maintained by the female hormones produced in the ovaries.

How to Tell Male and Female Gender in Betas

Although male and female bettas look similar when they are fry and juveniles, the differences between the two genders become more evident as they mature. When your bettas reach the age of about two months, you should easily be able to identify the gender characteristics that set them apart.

Using fin length to determine sex is not always reliable, and some breeds of betta have females with longer fins than average females. One should always check the other sex characteristics before assuming that your betta is a particular gender.

To confirm your betta’s sex, you should look for the ovaries. If your betta is dark, you can use a flashlight behind your fish to see the shadows of their organs. If you see merely the rounded shape of the stomach and nothing else, the chances are good that the betta is male.

Look for a dark triangular shape extending down towards the tail; you are probably looking at a female betta. Other differences between the betta genders are as follows.

Male Bettas 

Male bettas are the peacocks of the fish world with beautiful flowing fins in all colors of the rainbow. By comparison, the betta females appear pretty drab, with short fins and more muted colorations.

Male bettas are larger than females, with thicker bodies and longer fins. Male bettas have a fancy beard or operculum, a membrane under their gill covers that they flare when they want to intimidate another male.

Behaviorally the male stands out as more aggressive than the female betta. The breed didn’t get the name Siamese fighter fish for being cute and cuddly! Kind of like the modern pitbull breed, early domestication of the betta breed was used for a fishbowl version of pit fighting as a sport. Thus more aggressive males were favored and bred to enhance their fighting prowess.

Female Bettas 

Female bettas look quite drab next to the betta male showboats and are similar in length to the male but thinner in diameter. Although the female also has a membrane under her gill covers, it is usually held under the gills and not used in displays.

The female betta has a white spot at the base of her front (ventral) fins which is called an egg spot or ovipositor tube. The female releases her eggs from this tube during the mating process.

Betta Mating Process

When your bettas are ready to mate, the male beta will build a bubble nest and then attract a female to the nest. They engage in an elaborate and graceful mating ritual where the male embraces the female while she releases eggs while laid out in a classic Victorian ‘swoon.’

The male gently collects the eggs while the female recovers after multiple embraces and may attempt to eat her own eggs. Thus separation after mating is a must with these passionate pairs.

Closing Notes

While it is physiologically possible to change your female betta into a male, you might need steroids and a very tiny scalpel to conduct a mini hysterectomy. ( Please don’t, I am being facetious!). Studies show that a female can develop functioning male sexual organs, which means that it is not impossible for your betta to change sex. Just don’t hold your breath.